
(function(w){

    if( !( /iPhone|iPad|iPod/.test( navigator.platform ) && navigator.userAgent.indexOf( "AppleWebKit" ) > -1 ) ){
        return;
    }

    var doc = w.document;

    if( !doc.querySelector ){ return; }

    var meta = doc.querySelector( "meta[name=viewport]" ),
        initialContent = meta && meta.getAttribute( "content" ),
        disabledZoom = initialContent + ",maximum-scale=1",
        enabledZoom = initialContent + ",maximum-scale=10",
        enabled = true,
        x, y, z, aig;

    if( !meta ){ return; }

    function restoreZoom(){
        meta.setAttribute( "content", enabledZoom );
        enabled = true;
    }

    function disableZoom(){
        meta.setAttribute( "content", disabledZoom );
        enabled = false;
    }

    function checkTilt( e ){
        aig = e.accelerationIncludingGravity;
        x = Math.abs( aig.x );
        y = Math.abs( aig.y );
        z = Math.abs( aig.z );

        // If portrait orientation and in one of the danger zones
        if( !w.orientation && ( x > 7 || ( ( z > 6 && y < 8 || z < 8 && y > 6 ) && x > 5 ) ) ){
            if( enabled ){
                disableZoom();
            }
        }
        else if( !enabled ){
            restoreZoom();
        }
    }

    w.addEventListener( "orientationchange", restoreZoom, false );
    w.addEventListener( "devicemotion", checkTilt, false );

})( this );